1. Field of the Invention
The present invention relates to a cathode active material which is a component of a cathode material of a secondary aqueous lithium-ion battery (LIB), and a method for preparing the same.
2. Discussion of the Background
Sony Corporation first commercialized a non-aqueous lithium ion battery (LIB) in 1991. However, lithium cobalt oxide (LiCoO2), which is an anode active material constituting the non-aqueous LIB, is not appropriate to be used as an anode active material of a secondary LIB in a non-aqueous solution since its usable capacity is as low as about 150 mAh/g and Co metal costs too much.
Thus, studies have been conducted on anode active materials, such as LiNiO2, LiNi0.8Co0.2O2, LiMnO2, and V2O3, as a substitute for LiCoO2. Dahn et al. and Delmas et al. have recently focused on the research and development of new anode active materials using Li2MnO3, Li[Ni1/2Mn1/2]O2, LiNiO2, and LiCoO2.
The anode and cathode materials of the secondary non-aqueous LIB so far reported through the studies should demonstrate the charge/discharge performances also in the aqueous solution.
Dahn et al. first developed in 1994 a secondary aqueous LIB by using LiMn2O4 as an anode active material and VO2(B) as a cathode active material. The secondary aqueous LIB has a discharge energy density of 55 Wh/kg and a discharge potential of 1.5V with charge/discharge cycles of 25 times.
Wang et al. developed a secondary aqueous LIB using Li2Mn4O9 or Li4Mn5O12 as an anode active material and LiMn2O4 as a cathode active material. The secondary aqueous LIB has a discharge capacity of 100 mAh/g and an average discharge potential of 1.1 to 1.0V. However, the secondary aqueous LIB cannot be continuously used due to gases produced during its charge/discharge processes.
Hwang developed a secondary aqueous LIB using nano-sized ZnO-coated LiNiO2 as an anode active material and ZnxFeS2 as a cathode active material.